Magnetic beam switching cathode-ray tube



Feb. 4, 1969 L. KUSHNER MAGNETIC BEAM SWITCHING CATHODE-RAY TUBE Filed July 1, 1965 WT W RED-- o cnzszv- -BLUE- United States Patent Olfice 3,426,239 Patented Feb. 4, 1969 3,426,239 MAGNETIC BEAM SWITCHING CATHODE-RAY TUBE Lester L. Kushner, 5425 Gentry Ave., North Holywood, Calif. 91607 Filed July 1, 1965, Ser. No. 468,756 U.S. Cl. 315-21 Int. Cl. H01j 29/76 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to the control of electron beams, and particularly to means for effecting registration and color switching of electron scanning beams in color television image receiving tubes employing a perforated shadow mask structure:

Color television tubes of the cathode-ray type have 'been proposed having a luminescent screen containing a series of sequentially interspersed strips of different colored phosphors. In such tubes it is necessary to cause exact registration of the cathode-ray or electron beam with phosplhor strips of a given color in accordance with the original transmitted image. Otherwise, wrong color information would be produced.

Accordingly, it has been found desirable in beam registration systems to provide a control area between the luminescent screen and the shadow mask of a cathoderay tube. This control area may comprise a magnetic field which will respond to a suitable electrical waveform. By properly disposing such a magnetic field relative to the scanning path of the electron 'beam in accordance with the present invention, precise beam registration with color switching may be obtained.

The employment of a shadow :mask structure in cathoderay tubes will generally impose a severe limitation in the efficiency by which light may be generated by the image screen. Ignoring other factors, the screen efficiency may be related directly to the percentage of the total mask area open to the passage of the electron beam. The open area in the shadow masks used in present day color tubes is approximately 18 percent. This low percentage is largely due to a geometric pattern of round mask perforations commonly used in conjunction with the type of screen configuration employed therewith. According to the present invention the open area in the shadow mask is increased to 30 percent via the use of rectangular perforations in a pattern of novel configuration.

A primary object of this invention is to provide for improved reproduction of television images in substantially their natural color.

Another object of this invention is to provide improved control areas for effecting electron beam registration with predetermined screen positions in cathode-ray tubes.

Still another object of this invention is to provide an improvement of screen brightness in cathode-ray tubes of the type employing a shadow mask structure.

A further object of this invention is to provide means for color switching of an electron beam where a single electron gun is employed.

In the present invention a magnetic field is developed over the entire screen surface by passing a suitable electric current through a transparent conductive screen element. The magnitude and sense of the magnetic field is suitably controlled to precisely position the electron beam to predetermined screen positions.

The novel features that are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, as to its modes of operation along with additional features and advantages thereof will best be understood fiom a consideration of the following specification in conjunction with the accompanying drawings, in which:

FIGURE 1 is an exploded representation of a cathoderay tube showing in perspective sections of a laminated screen and a perforated shadow mask constructed in accordance with the invention;

FIGURE 2 illustrates overlaid sections of the shadow mask and screen, showing the relative positions of the screen phosphor strips and the mask perforations as viewed from the electron gun;

FIGURE 3 represents a modification of the laminated screen shown in FIGURE 1, with the phosphor lines omitted for clarity;

FIGURE 4 represents a preferred type of waveform for influencing the scanning beam and for controlling the cycle of operation.

Now referring to the drawings and in particular to FIGURE 1, a section of the shown cathode-ray screen 1 comprises a laminated structure consisting in part of a plurality of repeating, adjacently positioned and similar sized and arranged groups of strip-like phosphor elements, with each strip-like element of a group limited in its light representation to one different selected primary color, shown in the drawings as red 2, green 3 and blue 4. In a preferred form of the invention, said phosphor elements 2, 3 and 4 are deposited over a transparent electrically conductive coating 5 such as stannic oxide. The viewing surface of coating 5 is in turn deposited over a glass substrate 5a on the inner side of screen 1.

A shadow mask 6 having a multiplicity of rectangular perforations 7 is positioned with respect to the screen 1 and the scanning electron beam 8 as shown. Other elements of the cathode-ray tube include an electron gun 9 and a pair of beam scanning coils 10, said elements being disposed and operated in a manner well known to the industry.

Turning now to FIGURE 2, and with continued reference to FIGURE 1, a view from electron gun 9 is provided along the normal scanning path of electron beam 8 toward the shadow mask 6. Here, it may be seen that the rectangular perforations 7 are positioned with respect to the screen phosphor strips 2, 3, and 4 so as to allow electron beam 8 access to phosphor strips of one predetermined color. While the choice of the predetermined color is optional in the practice of the invention, the electron beam 8 will excite the green phosphor strip 3 as shown for the purpose of illustration. If the normal trajectory of the electron beam within the area between the shadow mask and the screen is not acted upon by further deflection, a green raster will, therefore, be produced by the scanning electron beam. The brightness of the scanned raster will depend largely upon the percentage of open area available in the shadow mask. It has been found that rectangular mask perforations used in the geometric pattern shown, and particularly in combination with the screen configuration shown, will yield a useful open area in the shadow mask of approximately 30 percent. This compares favorably with the 18 percent of open area available in shadow mask color television tubes currently used by the industry.

Returning once again to FIGURE 1, if a current is made to flow through the entire screen area of coating 5 in the direction shown by arrows 11, a magnetic field will be created around screen 1. This field will have a configuration as shown by a representative magnet flux line 12, a portion thereof comprising a control area 13 as shown. Upon entering said magnetic field within control area 13, the electron beam 8 will be deflected from its normal path toward green phosphor 3, and will therefore excite an adjacent phosphor of another color. For example, if current flows through coating 5 in an upward direction, the electron beam 8 will be deflected toward the red phosphor strip 2. Likewise, if the direction of current is reversed, the electron beam 8 will impinge upon blue phosphor 4. When the current falls to zero no magnetic field will exist around the screen area and the electron beam 8 will assume its normal trajectory toward the green phosphor 3.

Color switching and registration of the electron beam 8 to any one of the three phosphor strips 2, 3 and 4 may, therefore, be accomplished by passing a current of appropriate magnitude and waveform through coating 5.

Means for making suitable electrical connections with coating 5 are well known to the industry. Said connections being made along the top and bottom edges of coating 5 bordering screen 1 as shown. One such means is by employment of silver conducting bands 14. Said bands 14 may be fired onto the glass substrate 5a of coating 5 to ensure a permanent connection thereto.

A modification of the laminated screen 1 is illustrated in FIGURE 3, wherein fine closely spaced wires 15 are embedded into the glass substrate 5a. Said wires 15 may be substituted for the transparent conductive coating 5, said wires having the identical function aforedescribed with regard to coating 5.

In FIGURE 3 it may be seen that the magnetic flux 12 and the current path 11 are also the same as described with regard to FIGURES 1 and 2. Although the phosphor strips 2, 3 and 4 have been omitted in FIGURE 3 for the sake of clarity, it is understood that said phosphor strips are to be included, their having the same configuration and function as in FIGURES 1 and 2.

A current waveform suitable for employment in the practice of the invention is shown in FIGURE 4. In the drawing, that portion of the waveformhaving a positive polarity with respect to the zero axis will cause electron beam 8 to be deflected toward the red phosphor 2. Likewise, that portion of the waveform having a negative polarity below the zero axis will cause electron beam 8 to be deflected toward the blue phosphor 4. During the cycle where current is at Zero beam 8 will assume its normal trajectory toward the green phosphor 3. Although the invention is not limited thereto, the stairstep waveform shown will yield a maximum of beam dwell time t on the phosphor strips and it is, therefore, preferred. Since screen brightness will increase with increased dwell time of the electron beam, it is desirable that the rise time of the current waveform be made rapid in order to obtain maximum dwell time. The invention is particularly suited to respond to a rapid rise time due to the very low impedance characteristics of either coating 5 or wires 15, whichever is used. It is well known that fast response and a wide frequency band-Width are inherent with low impedance elements.

In accordance with the invention, therefore, a beam control area is provided directly adjacent to the screen to eifect color switching and to insure proper registration. Through the use of the present invention it is possible to produce a complete color television image by a single electron beam and at a single image surface.

A basic requirement for producing a color image is by synchronizing the aforedescribed sequential color switching of the electron beam with corresponding red, green and blue video signals obtained from a suitable color television receiver. The red, green and blue video signals are sampled sequentially to modulate the electron beam. In the same sequence, the waveform and magnitude of the current applied to coating 5 is controlled so that each color signal illuminates only its respective color phosphor.

Ways are known for providing sequential sampling of the received color information and for generating the aforementioned current waveform. Since this is not a part of the invention claimed, it need not be described.

Modifications and changes in addition to those mentioned herein will occur to those skilled in the art. All such modifications and changes within the spirit of the invention are intended to be embraced within the scope of the following claims.

I claim:

1. In a color-kinescope, containing in combination an electron scanning beam for developing an image by a scanning operation, a shadow mask structure disposed within the path of said electron beam, said shadow mask having a multiplicity of similar and repeating rectangular perforations, said perforations arranged in a plurality of of parallel and adjacently positioned rows, each of said rows being disposed within the electron beam path so as to correspond in their longest dimension with said screen phosphor strips of one predetermined color, means for registering said electron beam with the same said phosphor strips of one predetermined color, means for generating a magnetic field immediately adjacent to said screen in response to a controlling signal, said magnetic field to influence the path of said electron beam, means for switching the path of said electron beam to sequentially excite said screen phosphor strips of different designated colors one at a time in synchronism with said controlling signal, said electron scanning beam being intensity modulated in response to image signals representative of a component color image of the same component color being excited by said electron beam.

2. A kinescope for the reproduction of images in Substantially their natural color comprising in combination an image screen having plurality of repeating, adjacently positioned and similar groups of vertical strips of primary color representative phosphor materials and wherein each group of said strips includes at least one strip representative of the red color component, the green color component and the blue color component, an electron scanning beam for developing an image on said screen by a scanning operation, means for developing a controlling magnetic field within and adjacent to said screen, said magnetic field selectively directing the path of said electron beam to the said red, green and blue primary color representative phosphor strips in response to a controlling signal, a perforated shadow mask used in conjuction with said controlling magnetic field for effecting registration of said scanning electron beam on said screen, said shadow mask having a multiplicity of closely spaced rectangular perforations comprising a pattern of parallel and adjacently positioned vertical rows, said pattern being geometrically optimized to achieve maximum light emission from said screen.

References Cited UNITED STATES PATENTS 2,616,060 10/1952 Goodall 3l52l X 2,861,206 11/1958 Fiore et al l785.4 2,969,423 1/1961 Smith 315-21 X 3,016,474 1/1962 Hergenrother 31521 X RODNEY D. BENNETT, Primary Examiner.

BRIAN L. RIBANDO, Assistant Examiner.

US. Cl. X.R. 

